Jul 1, 2013

When Wholes Are Less Than Sums of the Parts

Headline national two party preferred results are clouding the dynamics and reality of what is happening at the state level - where elections are won and lost

Possum Comitatus — Editor of Pollytics

Possum Comitatus

Editor of Pollytics

Now that politics has reset itself, it’s probably worth looking at the polls since the change of PM – the results of which can pretty much be described as consensus

This is all very interesting and whatnot – Rudd poll boost, ALP becomes competitive etc etc…. see your nearest newspaper/blog for details.

But there’s something else worth talking about, and that’s what is going on underneath these topline national results.

Unless one side starts running away with the polling, or something weird happens in Qld like Rudd getting caught wearing a Blues jersey at the Origin decider, the headline two party preferred results may be a little misleading going in to the election – not in terms of them being wrong, but in terms of the seats that they would ordinarily deliver to each side. To understand why, we first need to look at what’s happening with Federal voting intention at the State level.

Both the Morgan SMS and ReachTEL polls had large sample sizes (5548 combined) and fortuitously we have the state breakdowns for each, allowing us to get a decent handle on the dynamics playing out at the State level. We also have an additional poll for Qld of 980 odd respondents which is not quite an internal poll, but it’s not quite not one either. It says the same things as the Qld components of ReachTEL and Morgan SMS (e.g ReachTEL has the ALP primary in Qld at 39.6, Morgan has it at 44 and the third party poll has the ALP primary sitting between them), so it’s all a much of a muchness – effectively just reducing our margin of error on the Qld numbers.

The “Swing to the ALP” figure is the change to the ALP two party preferred vote since the 2010 election. As we can see, there’s big movements to the ALP in Qld, but large movements away from them in Victoria and South Australia, with NSW and WA remaining static.

If we plug those numbers into Antony Greens Election Calculator, we get the ALP currently sitting on 77 seats, the Coalition 71 and 2 Independents (Katter and Wilkie). The Tasmania, ACT and NT results all come from small samples in either the ReachTEL or Morgan SMS results – so they’re a bit iffy, but you get the general picture.

My election simulation produces a similar result 76 seats to the ALP vs. 72 to the Coalition, with 2 Independents.

To understand how the ALP having a two party preferred national result of 48 or 49 can lead to getting a majority of seats, we need to look at what margins seats are sitting on in what states, and how swings in states produce wildly different seat gains/losses because of margin clustering.

The chart above shows the “swing to the ALP” half of the equation for LNP held seats on a 7% margin or less, or for seats requiring less than an ALP 60/40 average result in any state

Where each line crosses the bottom axis reflects what the ALP two party preferred result was at the 2010 election in each state – so WA (the black line) starts at 43.6%, Qld (the red line) starts at 44.9% etc. The points on each line represent a seat. As the ALP vote increases in each state, it shows roughly how many seats would be expected to fall to the ALP for a given change in two party preferred.

As you can see, with Qld coming off a relatively low base at the 2010 election, a 5% swing to the ALP would deliver around 9 seats to Labor in Qld simply because so many LNP held seats sit on relatively small margins. If the same swing occurred in WA it would only deliver 3 seats, in NSW 5 seats.

So  not only will Qld deliver more seats for a given swing than other states, we would also expect the swing in Qld to be larger than other states, simply because Rudd is PM (combined with the effect that his 2010 removal had on killing the ALP vote in Qld at the 2010 election)

Now let’s look at the other half of the equation – the swing away from the ALP

The big dangers here for Labor are NSW for any level of swing against them, and Victoria for relatively small swings.

In NSW, swings away from the ALP will catch seats on a 0.9% margin, then 1%, then 1.1%, then 1.5%, 2.7%, two on 4.2% and others on 4.4%, 5.1% and 5.2%

A 1.7% swing against the ALP in Victoria delivers 3 seats. But the next seat doesn’t fall on the pendulum after that until a swing of 5.8% against the ALP occurs.

So if the headline two party preferred results have underneath them big swings towards the ALP in Qld and relatively modest swings away from them in either NSW or Victoria (but not both), then we would expect to see the ALP win more seats than the national two party preferred might ordinarily suggest (for example, what we see now with the current polling).

This also tells is a little about the ALP’s path to 76 seats.

  1. Take Qld
  2. Either hold ground in both Victoria and NSW, or hold as much ground as possible in Victoria while aiming to make a few gains in NSW to offset probable losses like Dobell
  3. Take Qld

The major parties will start saying that the election will be won in Qld and NSW. For the ALP it will be taking Qld and holding NSW, for the Coalition it will be taking NSW and holding Qld. Yet considering that Qld is now much easier for the ALP, if Qld falls it goes a long way to balancing out any ALP losses in NSW and Victoria. If Qld falls one way and NSW the other, then things suddenly get really complicated.

Unless  someone breaks away in the polling.

But until or if they do, just keep an eye on the state breakdowns, because they’ll tell a more interesting and accurate story than the headline two party preferred figures.


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